(1) Field of the Invention
The present invention generally relates to packaging for circuit devices. More particularly, this invention relates to an electronic package and packaging method by which a leadframe is used to form electrical leads as well as thermal convectors for the package.
(2) Description of the Related Art
Semiconductor IC devices are at times enclosed in a protective housing to form an IC package, which can then be mounted on a circuit board or other suitable substrate using well known bonding techniques, such as soldering and brazing. The IC devices are typically mounted to a substrate or leadframe, and the resulting assembly is enclosed within a molded housing to form the IC package. Input/output (I/O) leads project through the walls of the housing and are electrically connected to the components within the housing by wire bonding or another suitable technique. The leads may be formed as part of a leadframe around which the housing is molded. Electronic components, typically active IC devices (e.g., transistors and diodes), are mounted on enlarged portions (“paddles”) of the leadframe. The package is then electrically connected and possibly mounted to a circuit board with the leads.
An example of an IC package that makes use of a leadframe is represented in FIGS. 1 and 2. FIG. 1 represents an intermediate process step showing an IC chip 112 mounted to a paddle 116 of a leadframe 114. The leadframe 114 further includes leads 118 and an outer support frame 120. FIG. 1 shows the leads 118 as having been separated from the paddle 116, and wire bonds 122 electrically connecting the leads 118 to bond pads 124 on the chip 112. FIG. 2 represents a cross-sectional view of a package 110 produced by overmolding the chip 112 and paddle 116 of FIG. 1 to produce an overmolded housing 126 from which the leads 118 protrude. FIG. 2 also depicts the package 110 following removal of the support frame 120 and forming of the leads 118 to permit mounting of the package 110 to a substrate.
IC devices generate heat during their operation, resulting in increased junction temperatures for the devices. Because IC reliability and function are adversely affected by high junction temperatures, many IC packages require features to remove heat from the IC device. Various solutions for removing heat from IC packages have been proposed. Most of these approaches involve placing the IC device in contact with a metal slug or an internal frame, which conduct thermal energy from the IC device to a surface of the package. Heat is then removed from the package surface by conduction into a separate heat sink or into the circuit board on which the package is mounted. In many existing concepts, thermal energy is eventually dissipated by convection into the surrounding air using fins thermally connected to the heat sink or circuit board.
While effective, the above approaches require secondary assembly processes and separate heat sinks, which add cost to the electronic assembly. It would be desirable to dissipate heat from an IC package having simplified construction and assembly requirements.